Method of making varnish of modified cyanate ester group curable resin composition, and prepreg, metal clad laminated board, film, printed circuit board, and multilayered circuit board using the composition

ABSTRACT

A modified cyanate ester group curable resin composition, and varnishes, prepregs, laminated boards adhered with metal foil, films, printed circuit boards, and multilayered circuit boards using the same, comprising: 
     (A) a cyanate ester group compound expressed by chemical formula (1),                    
     (where, R 1  is                    
     and respective of and R 2  and R 3  is any one of hydrogen or methyl group, and the both can be the same or different from each other, 
     (B) a monovalent phenolic group compound expressed by chemical formula (2), or formula (3),                    
     where R 4  and R 5  is any one of hydrogen atom or low alkyl group having 1 to 4 carbon atoms, and the both can be the same or different from each other, 
     n is a positive integer of 1 or 2.                    
      (where, R 6  is                    
     or                    
      (C) a polyphenylene ether resin, 
      (D) a flame retardant not reactive with the cyanate ester group compound, and 
      (E) a metal group reaction catalyst.

This application is a divisional application of Ser. No. 09/108,204,filed Jul. 1, 1998, now U.S. Pat. No. 6,156,831, issued Dec. 5, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to a modified cyanate ester group curableresin composition, and a varnish, prepreg, metal clad laminated board,film, printed circuit board, and multilayered circuit board using thesame.

A large volume of data is required to be processed with a high speed ina highly information-oriented society, and consequently the, frequencyof signals used in computers and information terminals has become higherand higher in recent years. However, since an electric signal has aproperty that its transmission loss becomes larger as the frequencybecomes higher, developing a low-loss printed circuit board capable ofcoping with such high frequencies has become an important requirement ofthe industry.

The transmission loss of a printed circuit board comprises a conductorloss depending on the shape of the circuit (conductor), a skin-effectresistance, a characteristic impedance, and the like, as well as adielectric loss depending on the dielectric properties of the insulatinglayer (dielectric) around the circuit. The dielectric loss is dominantin the overall electric loss in a high frequency circuit. Therefore, inorder to reduce the transmission loss of the high frequency circuit, itis apparent that reducing the dielectric constant and the dissipationfactor (tan δ) of the printed circuit board (particularly, theinsulating resin) is necessary. For example, in the field of mobilecommunication equipment dealing with high frequency signals, printedboards having a low dissipation factor are strongly required in order toreduce the transmission loss in a quasi-microwave band (1 to 3 GHz) asthe frequency of signals is increased.

On the other hand, in the field of electronic information equipment,such as computers the, development of high speed microprocessors havingan operating frequency exceeding 200 MHz and an increase of signalfrequency has been advancing rapidly in order to handle increasinlylarger volumes of information in a short time. In the equipment usingsuch high speed pulse signals the, signal delay time on the printedcircuit board becomes a problem. Since the signal delay time on theprinted circuit board becomes longer in proportion to the square root ofa specific dielectric constant ε r of the insulator around the circuit,resins having a low dielectric constant are required for circuit boardsused in a computer and the like.

Regarding resin compositions for improving the high frequency propertyof the printed circuit board and which are capable of coping with thetrend toward the use of increasingly higher frequency signals, asdescribed above, a method using a Cyanate ester/epoxy resin compositionhas been disclosed in JP-B-46-41112 (1971), and a method using abismaleimide/Cyanate ester/epoxy resin composition has been disclosed inJP B-52-31279 (1977), as a composition using a Cyanate ester resinhaving the lowest dielectric constant among thermosetting resins.

As a method of improving the high frequency property using athermoplastic resin, methods of using polyphenylene ether group resincompositions having a desirable dielectric property among heat-resistantthermoplastic resins, such as a resin composition composed of apolyphenylene ether resin (PPO or PPE) and a cross linkingpolymer/monomer has been disclosed in JP-B-5-77705 (1993), and a resincomposition composed of a polyphenylene ether having a specific curablefunctional group and a cross linking monomer has been disclosed inJP-B-6-92533 (1994).

Further, as a means of improving the high frequency property using aresin composition composed of a cyanate ester resin having a lowdielectric constant and a polyphenylene ether resin having a desirabledielectric property, a method of using it a resin composition composedof a cyanate ester/bismaleimide and a polyphenylene ether resin has beendisclosed in JP-B-63-33506 (1988), and a method of using a resincomposition composed of a phenol modified resin/cyanate ester reactantand polyphenylene ether resin has been disclosed in JP-A-5-311071(1993). Furthermore, a resin composition prepared by kneading apolyphenylene ether resin and a cyanate ester resin has been disclosedin JP-B-61-18937 (1986) as a heat resistant molding material having adesirable frequency characteristics.

The methods disclosed in JP-B-46-41112 (1971) and JP-B-52-31279 (1977),respectively, had a problem in that the high frequency property wasinsufficient though the dielectric constants were slightly lowered,because the resin compositions contained thermosetting resins other thana cyanate ester resin.

The methods disclosed in JP-B-5-77705 (1993) and JP-B-6-92533 (1994)also had a problem in that the resin compositions were high in moltenviscosity and lacked in resin flow, though their dielectric constantswere somewhat improved, because the main component of the resincompositions was a polyphenylene ether resin which was essentially athermoplastic resin. Therefore, the resin compositions required a hightemperature and a high pressure for pressurized molding of the laminatedboard, and were unsuitable for forming a multilayer printed circuitboard, which is required to fill a very small space in a circuitpattern, because of insufficient moldability.

The methods disclosed in JP-B-63-33506 (1988)and JP-A-5-311071 (1993)had a problem in that the high frequency property was stillinsufficient, though the dielectric constants were somewhat improved,because the thermosetting resin used together with the polyphenyleneether resin was a bismaleimide/cyanate ester resin or a phenol modifiedresin/cyanate ester reactant. When the quantity of polyphenylene etherresin was increased, the resin composition became high in moltenviscosity and lacked in fluidity, thereby to decrease the moldability,similar to the case of the polyphenylene group resin compositiondescribed above.

The resin composition prepared by kneading polyphenylene ether resin andcyanate ester resin disclosed in JP-B-61-18937 (1986) had a desirabledielectric property and a relatively preferable moldability, because themolten viscosity was-lowered by being modified by cyanate ester resin.However when cyanate ester was singly used as a curing composition, theproblem that the dielectric property of the cured resin had a highdissipation factor, while the dielectric constant was relatively low,was still remained. Further, when the quantity of cyanate ester wasdecreased (an adding quantity of polyphenylene ether resin wasincreased) in order to lower the dissipation factor, the problem thatthe molten viscosity of the resin composition was increased to make thefluidity insufficient still remained, and the moldability was decreased,as similar to the case of the polyphenylene group resin compositiondescribed above.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a modified cyanateester group curable resin composition having a desirable heatresistance, a similar moldability and workability as a conventionalthermosetting resin, such as an epoxy resin, a low dielectric property,and a low dissipation factor and a low loss property in the highfrequency band.

A second object of the present invention is to provide a flame retardantresin film using a modified cyanate ester group curable resincomposition, and a method for manufacturing the same.

An overall object of the present invention is to provide a resin filmusing a modified cyanate ester group curable resin composition, and amethod for manufacturing the same.

A third object of the present invention is to provide a modified cyanateester group curable resin varnish for a printed circuit board using amodified cyanate ester group curable resin composition, and a method formanufacturing the same.

A fourth object of the present invention is to provide methods ofmanufacturing prepreg for a laminated board and metal clad laminatedboard, using a modified cyanate ester group curable resin varnish.

A fifth object of the present invention is to provide a multilayeredcircuit board manufactured by laminating a printed circuit board and/oran inner layer circuit board, which are manufactured by patterning thecircuit on the laminated board manufactured by the above method ofmanufacturing prepreg for a laminated board and a metal clad laminatedboard, and for a prepreg, film, and/or a film adhered with metal foil,which are manufactured the above method, and forming circuits for makingconnections between inner circuits to each other and to the metal foil.

The first object of the present invention can be achieved with amodified cyanate ester group curable resin composition comprisingessentially (A) a cyanate ester group compound expressed by the chemicalformula (1), (B) a monovalent phenolic group compound expressed by anyone of the chemical formula (2) and (3), (C) a polyphenylene etherresin, (D) a flame retardant not reactive with the cyanate ester groupcompound and (E) a metal group reaction catalyst.

where, R₁ is

and respective of R₂ and R₃ is hydrogen or a methyl group, and both canbe the same or different from each other)

(where, respective of R₄ and R₅ is any one of a hydrogen atom and lowalkyl group having carbon number of 1 to 4, and both can be the same ordifferent from each other. n is a positive integer of 1 or 2.)

(where, R₆ is

or

It is preferable to use a modified cyanate ester group curable resincomposition, which is prepared by mixing (B) the monovalent phenolicgroup compound expressed by the chemical formula (2) or (3) at 4 to 30parts by weight with 100 parts by weight of (A) the cyanate ester groupcompound expressed by the chemical formula (1).

The second object of the present invention can be achieved by aflame-retardant resin film manufactured by semi-curing or curing amodified cyanate ester group curable resin composition including theflame-retardant not reactive with the cyanate ester group compound. Themethod of manufacturing the flame-retardant resin film can be achievedby a method comprising the steps of applying the varnish comprising themodified cyanate ester group curable resin composition including theflame retardant and a solvent onto one side plane of a carrier by aflowing method, and removing the solvent by heating and drying to formthe film.

The present invention can be also achieved by the modified cyanate estergroup curable resin film manufactured by semi-curing or curing themodified cyanate ester group curable resin composition, which does notinclude any flame-retardant not reactive with the cyanate ester groupcompound. The method of manufacturing the resin film can be achieved bya method

The third object of the present invention can be achieved with themodified cyanate ester group curable resin varnish comprisingessentially (F) an aromatic hydrocarbon group solvent, and (G) a ketonegroup solvent, in addition to the modified cyanate ester group curableresin composition. The method of manufacturing the varnish with themodified cyanate ester group curable resin composition for the printedcircuit board can be achieved by a method including the steps ofdissolving (C) polyphenylene ether resin into (F) the aromatichydrocarbon group solvent by heating, reacting subsequently (A) thecyanate ester group compound with (B) the monovalent phenolic groupcompound in the presence of (E) the metal group reaction catalyst in theabove solution to produce a mutually dissolving solution of the modifiedcyanate ester resin and the polyphenylene ether resin, and suspendingthe mutually dissolving resins by adding and agitating (G) the ketonegroup solvent.

The fourth object of the present invention can be achieved by the methodfor manufacturing prepreg for a laminated board, which Comprisesimpregnating the modified cyanate ester group resin varnish for aprinted circuit board into a substrate, and subsequently drying theimpregnated substrate at a temperature in the range of 80-200° C., andthe method for manufacturing a metal clad laminated board, whichcomprises piling up one or, plural prepregs for the laminated board,piling up one or plural metal foils at the upper and lower end planes ofthe pile, or either plane, and heating and pressurizing the pile to formthe metal clad laminated board.

The fifth object of the present invention can be achieved by a method ofmanufacturing a multilayered circuit board comprising the steps ofmanufacturing a printed circuit board by patterning circuits onto themetal clad laminated board manufactured by the above method forobtaining a metal clad laminated board, wherein the metal is plated ontoboth side planes and/or one side plane, with a conventional process suchas forming through-holes, metal plating, etching, and the like;laminating the prepreg, the film, or a combination of the prepreg andthe film, onto the surface of the printed circuit board as an innerlayer board, with a metal foil being further laminated thereon, byheating and pressurizing a pile of those materials; forming a window ata place on the metal foil, where a via-hole for connecting the innerlayer circuit and the outer layer circuit must be formed, using aphotosensitive resin or screen printing so that the metal foil at theplace where the via-hole must be formed is exposed; forming via-holesthrough to the inner layer circuit by a laser beam drilling processusing the metal foil as a mask after removing the metal foil exposed inthe window by etching; connecting the inner layer circuit and the outerlayer circuit by metal plating including the inner wall of thevia-holes; and manufacturing circuits onto an outer surface of the metalfoil to obtain the multilayered circuit board.

By repeating the above steps of the method of manufacturing amultilayered circuit board using the multilayered circuit boardmanufactured by the once-through operation of the above steps as theinner layer board, a multilayered circuit board having a large number oflayers can be manufactured.

Another multilayered circuit board can be manufactured by using a filmadhered with a metal foil instead of the prepreg and the film in theabove steps, piling up the film adhered with the metal foil onto innerlayer board so that the film plane is contacted with the inner layerboard, and applying heating and pressurizing to laminate them.

The dielectric property of a polymer material is strongly affected bythe polarization alignment of dipoles. Therefore, the dielectricconstant can be decreased by decreasing the number of polar groups inthe molecule, and the dissipation factor can be lowered by suppressingthe mobility of the polar groups. Since a cyanate ester resin produces asymmetric and rigid triazine structure when being cured, though it has astrong polar cyanate group, a cyanate ester resin can provide a curedmaterial having the lowest dielectric constant and dissipation factoramong the thermosetting resins.

However, in the actual curing reaction, the cyanate groups in the cynateester resin cannot all react to produce the triazine structure. Thereaction system gradually loses its fluidity as the curing reactionprogresses, and some cyanate groups remain in the system as non-reactedcyanate groups. As a result, only a cured resin having a dielectricconstant and dissipation factor values higher than what the cured resinshould essentially have was manufactured.

On the other hand, the resin composition in accordance with the presentinvention is aimed at decreasing the dielectric constant and thedissipation factor of the cured resin by adding an appropriate quantityof (B) monovalent phenolic group compound in order to convert theremaining non-reacted cyanate groups into imidocarbonate for decreasingthe polarity of the cured resin. A suitable material used for thispurpose is a chemical composition which is highly reactive with thecyanate group, and is single functional, relatively low in molecularweight, and mutually soluble with a cyanate ester resin (similar inmolecular structure). The monovalent phenolic group compounds used inthe resin composition of the present invention are specified by theabove reason.

Conventionally, a phenolic compound such as nonylphenol and the like wasused as an auxiliary catalyst for trimerizing reaction of cyanate ester(forming triazine rings) by adding approximately 1 to 2 parts by weightto 100 parts by weight of cyanate ester. However, since the amount addedwas actually a catalyst quantity, the effect of the phenolic compound todecrease the polarization by reacting with the cyanate group as abovewas not observed. According to the inventors' study of the addedquantity of the phenolic compounds, it was found that the dielectricconstant and the dissipation factor of the cured material could bedecreased by adding more of the phenolic compound than the conventionalquantity, and a decrease in heat resistance due to increase in the addedquantity of the phenolic compound could be suppressed by using aspecific monovalent phenolic group compound. Therefore, according to themethod of the present invention, it became possible to obtain a curedmaterial having a dielectric constant and a dissipation factor lowerthan those of the conventional cured materials of a single cyanate esterresin and the conventional cured material of resin composed of epoxyresin, a multivalent phenol group (hydroxyl in one side was apt toremain as a non-reacted group, which deteriorated the dielectricproperty), bismaleimide, and the like.

Therefore, in accordance with the modified cyanate ester group curableresin composition of the present invention, the added quantity of themonovalent phenolic group compound is important. That is, the monovalentphenolic group compound cannot react with all the non-reacted remainingcyanate group to decrease the polarization when the quantity added issmall, and the monovalent phenolic group compound itself remains asnon-reactants to deteriorate the dielectric property of the curedmaterial by the polarity of the hydroxyl of the monovalent phenolicgroup compound itself when the quantity added is more than necessary.

Further, in accordance with the modified cyanate ester group curableresin composition of the present invention, improving the dielectricproperty is intended by adding (C) the polyphenylene ether resin, whichis a thermoplastic resin having a desirable dielectric property, to themodified cyanate ester resin. The cyanate ester resin and thepolyphenylene ether resin are essentially not soluble with each other,and it is difficult to obtain a uniform resin. However, according to atechnique found by the inventors, when (A) the cyanate ester groupcompound and (B) the monovalent phenolic group compound were reacted ina solvent solution of polyphenylene ether resin, a uniform resinsolution could be manufactured by forming a so-called “semi-IPN(interpenetrating polymer network) resin”.

The flame retardant used in the resin composition of the presentinvention must be not reactive with the cyanate ester group compound soas not to interfere with the reaction between (A) the cyanate estergroup compound and (B) the monovalent phenolic group compound. Such aflame retardant is an alicyclic flame retardant (aliphatic ring typeflame retardant) which is a hydrocarbon group low polar composition andaccordingly it hardly deteriorates the dielectric property of the curedmaterial. Further, another kind of specified flame retardant is easilymiscible-with cyanate ester resin cured material because the specifiedflame retardant has a triazine structure similar to the cyanate estercured material, and the specified flame retardant can give a flameretardant effect to the cyanate ester cured material withoutdeteriorating the heat resistance and the dielectric property.

(A) A modified cyanate ester group curable resin composition inaccordance with the present invention comprises (A) a cyanate estergroup compound expressed by the chemical formula (1), (B) a monovalentphenolic group compound expressed by the chemical formula (2) or analkyl substituted phenolic compound expressed by the chemical formula(3), (C) a polyphenylene ether resin, (D) a flame retardant not reactivewith the cyanate ester group compound and (E) a metal group reactioncatalyst, as essential components.

In accordance with the present invention, (A) the cyanate ester groupcompound is a cyanate ester group compound having two cyanate groups inone molecule as expressed by the chemical formula (1). The chemicalcompounds expressed by the chemical formula (1) are, for example,bis(4-cyanato-phenyl)ethane; 2,2-bis(4-cyanato-phenyl)propane;bis(3,5-dimethyl-4-cyanato-phhenyl)methane;2,2-bis(4-cyanato-phenyl)-1,1,1,3,3,3-hexafluoropropane;α,α′-bis(4-cyanato-phenyl)-m-diisopropylbenzen; a cyanate ester compoundof phenol added dicyclopentadiene polymer; and the like. Among them, anyone or a mixture of 2,2-bis(4-cyanato-phenyl) propane andbis(3,5-dimethyl-4-cyanato-phenyl) methane is preferable, because abalance between the dielectric property and the moldability of theircured material is particularly desirable. The (A) the cyanate estergroup compounds can be used as a single kind or a mixture of two or morekinds.

In accordance with the present invention, (B) the monovalent phenolicgroup compound is a monovalent phenolic group compound expressed by thechemical formula (2) or an alkyl substituted phenolic compound expressedby the chemical formula (3), and a compound having desirable heatresistance is preferable. The chemical compound expressed by thechemical formula (2) is, for example, p-(α-cumyl) phenol, and thechemical compounds expressed by the chemical formula (3) are, forinstance, p-tert-butylphenol, p-tert-amylphenol, and p-tert-octylphenol.(B) the monovalent phenolic group compounds can be used by a single kindor a mixture of two or more kinds.

The added quantity of (B) the monovalent phenolic group compound in thepresent invention is desirably 4 to 30 parts by weight to 100 parts byweight of (A) the cyanate ester group compound, preferably 5 to 30 partsby weight, and more preferably 4 to 25 parts by weight. When the addedquantity of (B) the monovalent phenolic group compound is not more than4 parts by weight, a sufficient dielectric property cannot be attained,and the dissipation factor particularly in a high frequency band isgenerally not decreased sufficiently. On the other hand, when the addedquantity of (B) the monovalent phenolic group compound exceeds 30 partsby weight, the dissipation factor becomes rather high. This is notpreferable. Therefore, in order to obtain a cyanate ester group resincured material having a low dissipation factor in the high frequencyband provided by the present invention, an appropriate quantity of (B)the monovalent phenolic group compound must be added to (A) the cyanateester group compound.

In accordance with the present invention, (A) the cyanate ester groupcompound and (B) the monovalent phenolic group compound are used as themodified cyanate ester resin which is manufactured by reacting them.That is, they are used as a pre-polymer of (A) the cyanate ester groupcompound and imide-carbonated modified resin formed by adding (B) themonovalent phenolic group compound to (A) the cyanate ester groupcompound.

When (A) the cyanate ester group compound is reacted with (B) themonovalent phenolic group compound, the modified cyanate ester resin canbe manufactured by adding all the appropriate quantity of (B) themonovalent phenolic group compound to be reacted from the beginning ofthe reaction, or the modified cyanate ester resin can be manufactured byadding a part of the appropriate quantity of (B) the monovalent phenolicgroup compound at an initial stage of the reaction, and after cooling,adding the remaining amount of (B) the monovalent phenolic groupcompound at a B-stage reacting time or curing time.

In accordance with the present invention, (C) the polyphenylene etherresins are, for example, an alloyed polymer ofpoly(2,6-dimethyl-1,4-phenylene) ether, orpoly(2,6-dimethyl-1,4-phenylene) ether, with polystyrene, an alloyedpolymer of poly(2,6-dimethyl-1,4-phenylene) ether with styrene-butadienecopolymer, and the like. Particularly, the alloyed polymer ofpoly(2,6-dimethyl-1,4-phenylene) ether with polystyrene orstyrene-butadiene copolymer and the alloyed polymer ofpoly(2,6-dimethyl-1,4-phenylene) ether with styrene-butadiene copolymerare desirable. A polymer containing the alloyed polymer ofpoly(2,6-dimethyl-1,4-phenylene) ether of more than 50% by weight isdesirable, because the dielectric property of the cured material isdesirable, and more than 65% by weight is particularly preferable.

The added quantity of (C) the polyphenylene ether resin in the presentinvention is desirably 5 to 300 parts by weight to 100 parts by weightof (A) the cyanate ester group compound, preferably 10 to 200 parts byweight, and more preferably 15 to 100 parts by weight. When the addedquantity of (C) the polyphenylene ether resin is not more than 5 partsby weight, a sufficient dielectric property cannot attained. On theother hand, when the added quantity of (C) the polyphenylene ether resinexceeds 300 parts by weight, the moldability is deteriorated, becausethe molten viscosity becomes high and the fluidity becomes low, and thereactivity with (A) the cyanate ester group compound is alsodeteriorated.

In accordance with the present invention, (D) examples of the flameretardant not reactive with the cyanate ester group compounds are, forexample, 1, 2-dibromo-4-(1, 2-dibromoethyl) cyclohexane,tetrabromocyclohexane, hexabromocyclododecane, polybromodiphenylether,polystyrene bromide, polycarbonate bromide, and triphenylcyanate bromidegroup flame retardants expressed by the chemical formula (4), and thelike. Particularly, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane;tetrabromocyclooctane; hexabromocyclododecane; 2,4,6-tris(tribromophenoxy)-1,3,5-triazine are desirable, because the manufacturedcured materials have preferable dielectric properties.

(where, respective of 1, m, and n is an integer of 1 to 5, and theintegers can be the same or different from each other.)

The added quantity of (D) the flame retardant not reactive with thecyanate ester group compounds of the present invention is desirably 5 to30 parts by weight to 100 parts by weight of the total of (A) thecyanate ester group compound, (B) the monovalent phenolic group compoundand (C) the polyphenylene ether resin, and preferably 5 to 20 weightpart, and further preferably 10 to 20 parts by weight. When the addedquantity of (D) the flame retardant not reactive with the cyanate estergroup compound is not more than 5 parts by weight, the flame retardanteffect is insufficient. When the added quantity of (D) the flameretardant exceeds 30 parts by weight, the heat resistance of the resinis decreased.

In accordance with the present invention, (E) the metal group reactioncatalyst accelerates the reaction between (A) the cyanate ester groupcompound and (B) the monovalent phenolic group compound, and is used asthe reaction catalyst in manufacturing the modified cyanate ester groupcurable resin composition and as the curing accelerator in manufacturingthe laminated board. The metal group reaction catalysts being used aremetallic catalysts such as manganese, iron, cobalt, nickel, copper, andzinc. Practically, the catalysts are used as an organic acid metal saltcompound such as 2-ethylhexanoic salts, naphthenic salts, and as anorganic metal complex such as acetylacetone complex. The same kind ofthe metal group reaction catalyst can be solely used or two or morekinds of the metal group reaction catalysts can be respectively used asthe reaction catalyst in manufacturing the modified cyanate ester groupcurable resin composition and as the curing accelerator in manufacturingthe laminated board.

The added quantity of (E) the metal group reaction catalyst of thepresent invention is desirably 1 to 300 ppm to 1 (g) of (A) the cyanateester group compound, preferably 1 to 200 ppm, and more preferably 2 to150 ppm. When the added quantity of (E) the metal group reactioncatalyst is not more than 1 ppm, the reactivity and the curabilitybecome insufficient. On the other hand, when the added quantity exceeds300 ppm, the reaction becomes difficult to control and the moldabilityis deteriorated, because the curing speed becomes too fast to becontrolled. The timing for adding (E) the metal group reaction catalystof the present invention can be at the time of manufacturing themodified cyanate ester group curable resin composition when thenecessary quantity of the metal group reaction catalyst as a reactionaccelerator and a curing accelerator is added together at a time, or atthe time of manufacturing the modified cyanate ester group curable resincomposition when the quantity of the metal group reaction catalystnecessary for accelerating the denaturalizing reaction is added and thenat the time after completion of the reaction when the remaining catalystor the other metallic catalyst is added and mixed as a curingaccelerator.

An inorganic filler and other additives other than the above-mentionedessential components can be added to the modified cyanate ester groupcurable resin composition of the present invention. The usable fillersare silica, alumina, aluminum hydride, calcium carbonate, clay, talk,silicon nitride, boron nitride, titanium oxide, barium titanate, leadtitanate, strontium titanate and the like. In accordance with thepresent invention, the quantity to be added is preferably less than 250parts by weight to 100 parts by weight of the total resin composition,in order to obtain a uniform distribution in the adhered quantity of theresin and a desirable appearance when the resin varnish of the presentinvention is impregnated into the supporting material such as glasscloth.

The modified cyanate ester group curable resin composition of thepresent invention is used in manufacturing flame retardant films, films,other varnishes, prepregs for laminated board, and metal clad laminatedboards, for example, in a manner as described below. That is, initially,the prepreg is manufactured by dissolving or suspending the modifiedcyanate ester group curable resin composition of the present inventioninto a solvent to form a varnish, impregnating the varnish into a basematerial such as glass cloth, and then drying the impregnated basematerial. Next, the metal clad laminated board with metallic films onboth side surfaces or with a metallic film on one side surface ismanufactured by laminating one or an arbitrary number of sheets of theprepreg, laminating metallic films on both sides surfaces or on one sidesurface of the laminated prepreg; and then heating and pressurizing thelaminated prepreg. The flame retardant films and films can bemanufactured by semi-curing or curing the modified cyanate ester groupcurable resin composition of the present invention.

Practical examples of the solvents used for making the varnish of themodified cyanate ester group curable resin composition in accordancewith the present invention are an aromatic hydrocarbon having a boilingpoint in the range of 70-170° C. such as benzene, toluene, xylene andthe like, a hydrocarbon halide such as trichloroethylene, chlorobenzene,and the like, an amide group such as N, N-dimethyl formaldehyde, N,N-dimethylacetoamide, and the like, and nitrogen group solvents such asN-methylpyrolidone and the like. Particularly, aromatic hydrocarbon suchas benzene, toluene, xylene, and the like are desirable. These solventscan be used as solely one kind or by mixing two or more kinds. The addedquantity of the aromatic hydrocarbon is desirably 150 to 500 parts byweight to 100 parts by weight of (C) the polyphenylene ether resin,preferably 150 to 400 parts by weight, and more preferably 150 to 300parts by weight.

Ketones having a boiling point in the range of 50-170° C. such asacetone, methylethylketone, methy-lisobutylketone, cyclohexanone, andthe like have a low solubility to the modified cyanate ester groupcurable resin composition, but have such an advantage that when theketones are used together with the above-mentioned solvents, a highdensity and low viscosity solution can be manufactured by forming asuspension of the resin composition in accordance with the presentinvention. From this viewpoint, the solvents used for making the varnishof the modified cyanate ester group curable resin composition inaccordance with the present invention are desirably mixed solvents of anaromatic hydrocarbon such as benzene, toluene, xylene, and the like,with ketones such as acetone, methylethylketone, methy-lisobutylketone,cyclohexanone, and the like. The quantity of the ketone to be added isdesirably 50 to 500 parts by weight to 100 parts by weight of theorganic hydrocarbon group solvent, preferably 50 to 400 parts by weight,and more preferably 50 to 300 parts by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

No drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, details of the present invention will be explainedreferring to preferred embodiments.

The modified cyanate ester group curable resin composition varnisheswere manufactured in accordance with the composition indicated in Table1.

Embodiment 1

Toluene 450 g, and PKN 4752 (a trade name of a product of Japan GEPlastic Co.) 210 g as (C) a polyphenylene ether resin were charged intoa 5-liter 4-nozzle separable flask provided with a thermometer, acooling pipe, and the mixture was a stirrer, and heated to 80° C. withstirring so as to be dissolved. Next, 2,2-bis(4-cyanatophenyl) propane(Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 gas (A)the cyanate ester group compound; p-(α-cumyl) phenol (a product of SunTechnochemical Co.) 64 g as (B) the monovalent phenolic group compound;triphenylcyanulate bromide (Pyroguard SR-245, a trade name of a productof Dai-ichi Industrial Chemical Co.) 135 g as (D) the flame retardantnot reactive with the cyanate ester group compounds were charged intothe separable flask so as to be dissolved, and then 4 g of a toluenesolution of 10% by weight of cobalt naphthenate (content of Co=8% byweight, a product of Japan Chemical Industry Co.) was added to thereaction liquid at a reflux temperature for 1 hour. Subsequently, thereaction liquid was cooled. When the inner temperature became 90° C.,methyl ethyl ketone (MEK) 600 g was charged into the separable flaskwith stirring to form a suspension. After further cooling the reactionliquid to room temperature, 1 g of a toluene solution of 10% by weightzinc naphthenate (content of Zn=8% by weight, a product of JapanChemical Industry Co.) was added and dissolved by stirring to obtain avarnish (solid content=51 weight %)

Embodiment 2

Toluene 300 g and polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 140 g were charged into a 5-liter4-nozzle separable flask provided with a thermometer, a cooling pipe andthe mixture was a stirrer, and heated to 80° C. so as to be dissolvedwith stirring. Subsequently, 2,2-bis(4-cyanatophenyl) propane (ArocyB-10, a trade name of a product of Asahi Ciba Co.) 700 g; p-(α-cumyl)phenol (a product of Sun Technochemical Co.) 10 g; triphenylcyanulatebromide (Pyroguard SR-245, a trade name of a product of Dai-ichiIndustrial Chemical Co.) 125 g were charged into the separable flask soas to be dissolved, and then 3 g of a toluene solution of 10% by weightmanganese naphthenate (content of Mn=8% by weight, a product of JapanChemical Industry Co.) was added to the reaction liquid at a refluxtemperature for 1 hour. subsequently, the reaction liquid was cooled.When the inner temperature became 90° C., methyl ethyl ketone (MEK) 600g was charged into the separable flask with stirring to form asuspension. After further cooling the reaction liquid to roomtemperature, 75 g of p-(α-cumyl) phenol and 1 g of a toluene solution of10% by weight zinc naphthenate (content of Zn=8% by weight, a product ofJapan Chemical Industry Co.) was added and dissolved with stirring toobtain a varnish (solid content=8% by weight).

Embodiment 3

Toluene 300 g and polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 80 g were charged into a 5-liter4-nozzle separable flask provided with a thermometer, a cooling pipe,and the mixture was a stirrer so as, and heated to 80° C. with stirringto be dissolved. Subsequently,α,α′-bis(4-cyanatophenyl)-m-diisopropylbenzen (RTX-366, a trade name ofa product of Asahi Ciba Co.) 800 g; and p-(α-cumyl) phenol (a product ofSun Technochemical Co.) 10 g were charged into the separable flask so asto be dissolved , and then 2 g of a toluene solution of 10% by weightiron naphthenate (content of iron=5% by weight, a product of JapanChemical Industry Co.) was added to the reaction liquid at a refluxtemperature for 1 hour. Then, tetrabromocyclooctane (Saytex BC-48, atrade name of a product of Albemarl Co.) 110 g was added into the flaskand dissolved. Subsequently, the reaction liquid was cooled. When theinner temperature became 90° C., methyl ethyl ketone (MEK) 600 g wascharged into the separable flask with stirring to form a suspension.After further cooling the reaction liquid to room temperature, 75 g ofp-(α-cumyl) phenol and 2 g of a toluene solution of 10% by weight coppernaphthenate (content of copper=8% by weight, a product of Japan ChemicalIndustry Co.) were added into the flask and dissolved with stirring toobtain a varnish (solid content=54% by weight).

Embodiment 4

Toluene 600 g and polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 300 g were charged into a 5-liter4-nozzle separable flask provided with a thermometer, a cooling pipe,and the mixture was a stirrer, and heated to 80° C. with stirring so asto be dissolved. Next, bis(3,5-dimethyl-4-cyanato-phenyl) methane (ArocyM-10, a trade name of a product of Asahi Ciba Co.) 600 g; andp-(α-cumyl) phenol (a product of Sun Technochemical Co.) 30 g werecharged into the separable flask so as to be dissolved , and then 4 g ofa toluene solution of 10% by weight cobalt naphthenate (content of Co=8%by weight, a product of Japan Chemical Industry Co.) was added to thereaction liquid at a reflux temperature for 1 hour; and thenhexabromocyclododecane (CD-75P, a trade name of a product of Grate LakesCo.) 150 g was added into the flask and dissolved. Subsequently, thereaction liquid was cooled. When the inner temperature became 90° C.,methyl ethyl ketone (MEK) of 750 g was charged into the separable flaskwith stirring to form a suspension. After further cooling the reactionliquid to room temperature, 120 g of p-(α-cumyl) phenol was added anddissolved with stirring to obtain a varnish (solid content=47% byweight).

Embodiment 5

Toluene 750 g and polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 400 g were charged into a 5-liter4-nozzle separable flask provided with a thermometer, a cooling pipe andthe mixture was a stirrer, and heated to 80° C. with stirring so as tobe dissolved. Next, 2,2bis(4-cyanatophenyl)-1,1,1,3,3,3-hexafluoropropane (Arocy F-10, a tradename of a product of Asahi Ciba Co.) 500 g; and p-(α-cumyl) phenol (aproduct of Sun Technochemical Co.) 28 g were charged into the separableflask to be dissolved, and then 6 g of a toluene solution of 10% byweight copper naphthenate (content of Cu=5 96 by weight, a product ofJapan Chemical Industry Co.) was added to the reaction liquid at areflux temperature for 1 hour; and then 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (Saytex BCL-462, a trade name of a product of Albemarl Co.)150 g was added into the flask and dissolved. Then, the reaction liquidwas cooled. When the inner temperature became 90° C., methyl ethylketone (MEK) 500 g was charged into the separable flask with stirring toform a suspension. After further cooling the reaction liquid to roomtemperature, 1 g of a toluene solution of 10% by weight manganesenaphthenate (content of Mn=8% by weight, a product of Japan ChemicalIndustry Co.) was added into the flask and dissolved with stirring toobtain a varnish (solid content=46% by weight).

Embodiments 6-10

The varnishes in the embodiment 6-10 were manufactured by the samemethod under the same condition as described in the above embodiments1-5 except only for replacing the component (B) the monovalent phenolicgroup compound with the compounds indicated in the embodiments 6-10 ofTable 1, respectively.

Comparative Example 1

Toluene 1800 g, polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 210 g, 2,2-bis(4-cyanato-phenyl)propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g,and 2,2-bis (4-hydroxyphenyl) propane (BPA; bisphenol A, a product ofMitsui Toatsu Chemicals, Inc.) 69 g instead of p-(α-cumyl) phenol in theembodiment 1, were charged into the separable flask, and were stirred tobe dissolved. Then, 3 g of a toluene solution of 10% by weight cobaltnaphthenate (content of Co=8% by weight, a product of Japan ChemicalIndustry Co.) was added to the reaction liquid at a reflux temperaturefor 1 hour. Next, bromated bisphenol A type epoxy resin (ESB 400, atrade name of a product of Sumitomo Chemicals Co., Ltd.) 200 g as aflame retardant reactive with cyanate group was charged into theseparable flask to be dissolved, and the reaction liquid was cooled.However, because the reaction liquid was solidified (into a greasestate) near room temperature, toluene of 1200 g was further added andwas stirred to dissolve the reaction product to obtain a varnish (solidcontent=28% by weight).

Comparative Example 2

Toluene 1800 g, polyphenylene ether resin (PKN 4752, a trade name of aproduct of Japan GE Plastic Co.) 210 g, 2,2-bis(4-cyanato-phenyl)propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 700 g,and nonylphenol (a product of Mitsui Toatsu Chemicals, Inc.) 11 ginstead of p-(α-cumyl) phenol in the embodiment 1 were charged into theseparable flask, and were stirred so as to be dissolved. Then, 4 g of atoluene solution of 10% by weight cobalt naphthenate (content of Co=8 $by weight, a product of Japan Chemical Industry Co.) was added to thereaction liquid at a reflux temperature for 1 hour. Next, bromatedbisphenol A type epoxy resin (ESB 400, a trade name of a product ofSumitomo Chemicals Co., Ltd.) 190 g as a flame retardant reactive withcyanate group was charged into the separable flask to be dissolved, andthe reaction liquid was cooled. However, because the reaction liquid wassolidified (into a grease state) near room temperature, toluene 900 gwas further added and was stirred to dissolve the reaction product toobtain a varnish (solid content=29% by weight).

Comparative Example 3

Toluene 1500 g, and polyphenylene ether resin (PKN 4752, a trade name ofa product of Japan GE Plastic Co.) 210 g were charged into the separableflask, and were stirred so as to be dissolved. Next, an oligomer of2,2-bis(4-cyanatophenyl) propane (Arocy B-30, a trade name of a productof Asahi Ciba Co.) 700 g instead of 2,2-bis(4-cyanato-phenyl) propane(Arocy B-10, a trade name of a product of Asahi Ciba Co.) in theembodiment 1; nonylphenol (a product of Mitsui Toatsu Chemicals, Inc.)67 g instead of p-(α-cumyl) phenol; and bromated bisphenol A type epoxyresin (ESB 400, a trade name of a product of Sumitomo Chemicals Co.,Ltd.) 200 g as a flame retardant reactive with cyanate group were letinto the separable flask; were charged into the flask, heated anddissolved at 80° C. for 1 hour. Then, the reaction liquid was cooled toroom temperature, and 2 g of a toluene solution of 10% by weight zincnaphthenate (content of Zn=8% by weight, a product of Japan ChemicalIndustry Co.) was added into the flask to obtain a varnish (solidcontent=44% by weight). However, flocculated separation of polyphenyleneether resin was observed in the resin varnish after two days elapsed.

Comparative Example 4

In embodiment 4, toluene 1600 g, polyphenylene ether resin (PKN 4752, atrade name of a product of Japan GE Plastic Co.) 300 g,bis(3,5-dimethyl-4-cyanatophenyl) methane (Arocy M-10, a trade name of aproduct of Asahi Ciba Co.) 600 g, and nonylphenol of 9 g instead ofp-(α-cumyl) phenol (a product of Sun Techno Chemical Co.) were chargedinto the separable flask, and were stirred so as to be dissolved. Then,3 g of a toluene solution of 10% by weight manganese naphthenate(content of Mn=8% by weight, a product of Japan Chemical Industry Co.)was added to the reaction liquid at a reflux temperature for 1 hour.Next, tetrabromobisphenol A (Fire Guard FG-2000, a trade name of aproduct of Teijin Chemicals co., Ltd.) 150 g as a flame retardantreactive with cyanate group was charged into the separable flask so asto be dissolved, and the reaction liquid was cooled. However, becausethe reaction liquid was solidified (into a grease state) near roomtemperature, toluene 1200 g was further added and was stirred todissolve the reaction liquid to obtain a varnish (solid content=27% byweight).

TABLE 1 (E) (A) (B) (C) (D) Metallic Cyanate Monovalent Polypheny- Flamereaction ester phenol lene ether retardant catalyst Emb¹⁾ Com²⁾ Mix³⁾Com. Mix. Com. Mix. Com. Mix. Com. Mix. 1 B-10 700 PCP 64 PPO 210 SR-135 Co 4 245 Zn 1 2 B-10 700 PCP 10 PPO 140 SR- 125 Mn 3 PCP 75 245 Zn 13 RTX- 800 PCP 10 PPO 80 BC-48 110 Fe 2 366 PCP 75 Cu 2 4 M-10 600 PCP30 PPO 300 CD- 150 Co 4 PCP 120 75P 5 F-10 500 PCP 28 PPO 400 BCL- 150Cu 6 462 Mn 1 6 B-10 700 POP 62 PPO 210 SR- 135 Co 4 245 Zn 1 7 B-10 700POP 10 PPO 140 SR- 125 Mn 3 POP 73 245 Zn 1 8 RTX- 800 PBP 10 PPO 80BC-48 110 Fe 2 366 PBP 51 Cu 2 9 M-10 600 POP 30 PPO 300 CD- 150 Co 4POP 115 75p 10 F-10 500 PAP 21 PPO 400 BCL- 150 Cu 6 462 Mn 1 C-1⁴⁾ B-10700 BPA 69 PPO 210 ESB- 200 Co 3 400 C-2 B-10 700 NP 11 PPO 210 ESB- 190Co 4 400 C-3 B-10 700 NP 67 PPO 210 ESB- 200 Zn 2 400 C-4 M-10 600 NP 9PPO 300 TBA 150 Mn 3

Remarks:

1) Emb; Embodiment number

2) Com.; Kind of compound

3) Mix.; Mixing ratio (parts by weight)

4) C-; Comparative example number

(A) B-10 (a product of Asahi Ciba Co.); 2,2-bis(4-cyanatophenyl) propane

M-10 (a product of Asahi Ciba Co.); bis(3,5-dimethyl-4-cyanatophenyl)methane

F-10 (a product of Asahi Ciba Co.); 2,2bis(4-cyanatophenyl)-1,1,1,3,3,3-hexafluoropropane

RTX-366 (a product of Asahi Ciba Co.);α,α′-bis(4-cyanatophenyl)-m-diisopropylbenzen

(B) PCP (a product of Sun Technochemical Co.); p-(α-cumyl)phenol

BPA (bisphenol A, a product of Mitsui Toatsu Chemicals, Inc.);2,2-bis(4-hydroxyphenyl) propane

NP (a product of Mitsui Toatsu Chemicals, Inc.); nonylphenol

PBP (a product of Wako Pure chemical Co.); p-tert-bytulphenol

PAP (a product of Wako Pure chemical Co.); p-tert-amylphenol

POP (a product of Wako Pure chemical Co.); p-tert-octylphenol

(C) PPO (PKN 4752, a trade name of a product of Japan GE Plastic Co.);polyphenylene ether

(D) BCL-462 (a trade name of a product of Albemarl Co.);1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane

BC-48 (a trade name of a product of Albemarl Co.); tetrabromocyclooctane

CD-75P (a trade name of a product of Grate Lakes Co.);hexabromocyclododecane

SR-245 (a trade name of a product of Dai-ichi Industrial Chemical Co.);2,4,6-tris(tribromophenoxy)-1,3,5-tryazine

ESB-400 (a trade name of a product of Sumitomo Chemicals Co., Ltd.);bromated bisphenol A type epoxy resin

TBA (FG-2000, a trade name of a product of Teijin Chemicals Co., Ltd.);tetrabromobisphenol A

(E) Co; toluene solution of 10% by weight cobalt naphthenate (content ofCo=8% by weight, a product of Japan Chemical Industry Co.)

Zn; toluene solution of 10% by weight zinc naphthenate (content of Zn=8%by weight, a product of Japan Chemical Industry Co.)

Mn; toluene solution of 10% by weight manganese naphthenate (content ofMn=8% by weight, a product of Japan Chemical Industry Co.)

Fe; toluene solution of 10% by weight iron naphthenate (content of Fe=5%by weight, a product of Japan Chemical Industry Co.)

Cu; toluene solution of 10% by weight copper naphthenate (content ofCu=5% by weight, a product of Japan Chemical Industry Co.)

A prepreg having an adhered resin, of which the quantity was 40 to 45%by weight, was manufactured by impregnating an E glass cloth having athickness of 0.2 mm (weight 209 g/m²) with the manufactured resinvarnish and heating it at 140° C. for 5 to 10 minutes(so that thegelling time (170° C.) became 5 to 7 minutes). In the cases of the resinvarnish of comparative examples 1,2, and 4, the prepregs having anadhered resin, of which the quantities were in the range of 40 to 45% byweight, were manufactured by repeating the impregnation applying worktwice, because the solid content was low. In the prepreg of comparativeexample 3, separation between the cyanate ester resin and thepolyphenylene ether resin was observed.

Next, laminated boards with copper foil were manufactured by laminatingfour prepregs and copper foils having a thickness of 18 μm on bothsides, pressurizing the boards to form the laminated board under acondition of 170° C., 2.5 MPa for 60 minutes, and then performing a heattreatment at 230° C. for 120 minutes. Using the manufactured laminatedboards with copper foil, the dielectric property, the resistance toheated solder, the peeling strength of the copper foil and the flameretardant property were measured in accordance with the followingmethods. The results are shown in Table 2.

Methods of evaluating properties

Specific dielectric constant and dissapation factor/ 1 GHz: theproperties were measured through the tri-plate structure straight wiringresonance method.

Resistance to heated solder: an outer appearance was inspected byholding a test piece, of which the copper foils were removed, in a PCT(121° C., 0.22 MPa), and then immersing the test piece into a moltensolder at 260° C. for 20 seconds. In the table, “OK” means no occurrenceof measling nor swelling, and “NG” means occurrence of measling andswelling.

Peeling strength of copper foil: Measurement was performed in accordancewith JIS-C-6481.

Flame retardant resistance: Measurement was performed in accordance withUL-94 Vertical Test Method.

TABLE 2 Dielect.²⁾ Solder³⁾. P.S.⁴⁾ of Flame Remarks: prop./1 GHz. heatres. Cu foil retard.⁵⁾ Sol.ct.⁶⁾ Emb¹⁾ D.c. D. f. 260° C., 20 s. (kN/m)UL-94 of v. (%) 1 3.5 0.0045 PCT 4 h OK 1.5 V-0 51 2 3.5 0.0048 PCT 4 hOK 1.7 V-0 54 3 3.3 0.0038 PCT 4 h OK 1.7 V-0 54 4 3.4 0.0042 PCT 3 h OK1.4 V-0 47 5 3.3 0.0039 PCT 3 h OK 1.3 V-0 46 6 3.5 0.0045 PCT 4 h OK1.5 V-0 51 7 3.5 0.0048 PCT 3 h OK 1.7 V-0 54 8 3.3 0.0040 PCT 3 h OK1.6 V-0 54 9 3.4 0.0043 PCT 3 h OK 1.4 V-0 47 10 3.3 0.0041 PCT 3 h OK1.3 V-0 46 C-1 3.9 0.0106 PCT 2 h OK 1.4 V-0 28(apply twice) C-2 3.90.0092 PCT 2 h OK 1.4 V-0 29(apply twice) C-3 3.8 0.0099 PCT 1 h OK 1.1V-0 44(PPO separatd) C-4 3.8 0.0088 PCT 1 h OK 1.3 V-0 27(apply twice)

Remarks:

1) Emb.: Embodiment number

2) Dielect. prop./1 Ghz: Dielectric properties/1 Ghz.

D. c.: Dielectric constant

D. f.: Dissipation factor

3) Solder. Heat res.: Soldering heat resistance

4) P.S. of Cu foil: Peeling strength of copper foil

5) Flame retard.: Flame retardant

6) Sol.ct. of v.: Solid content of varnish

It is clear from Table 1 that all of the laminated board using themodified cyanate ester group curable resin compositions of embodiments 1to 10 have a low dielectric constant, a low dissipation factor at 1 GHz,a desirable soldering heat resistance with absorbed moisture, and adesirable peeling strength of the copper foil. On the contrary, thelaminated boards of the comparative examples have a high dielectricconstant, a high dissipation factor at 1 GHz, and low heat resistance.

Embodiments 11-18, comparative examples 5-7

In accordance with the same method as the embodiment 1, a modifiedcyanate ester group curable resin composition varnish was manufacturedwith the composition indicated as embodiment 11 in Table 3.

Toluene 360 g, and polyphenylene ether resin (nonylPKN 4752, a tradename of a product of Japan GE Plastic Co.) 160 g were charged into a1-liter 4-nozzle separable flask provided with a thermometer, a coolingpipe, and the mixture was a stirrer, and heated to 80° C. with stirringso as to be dissolved. Next, after charging 2,2-bis(4-cyanatophenyl)propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 80 g,and p-(α-cumyl) phenol (a product of Sun Technochemical Co.) 2 g intothe flask so as to be dissolved, 0.3 g of a toluene solution of 10% byweight of manganese naphthenate (content of Mn 8% by weight, a productof Japan Chemical Industry Co.) was added to the reaction liquid, andreacted at a reflux temperature for 3 hours. Then,tetra-bromocyclooctane (Saytex BC-48, a trade name of a product ofAlbemarl Co.) 60 g was added into the flask and dissolved. Subsequently,the reaction liquid was cooled. When the inner temperature became 90°C., methyl ethyl ketone (MEK) 600 g was charged into the separable flaskwith stirring to form a suspension. After further cooling the reactionliquid to room temperature, p-(α-cumyl) phenol 6 g, and a toluenesolution of 10% by weight zinc naphthenate (content of Zn=8% by weight,a product of Japan Chemical Industry Co.) 0.2 g were added and dissolvedby stirring to obtain a modified cyanate ester group curable resincomposition varnish (solid content=32 weight %).

Similarly, the modified cyanate ester group curable resin compositionvarnish of embodiment 12 was manufactured using the compositionindicated as embodiment 12 in Table 3.

Using the composition indicated as embodiment 13 in Table 3, themodified cyanate ester group curable resin composition varnish ofembodiment 12 was manufactured.

Toluene 540 g, and polyphenylene ether resin (nonylPKN 4752, a tradename of a product of Japan GE Plastic Co.) 105 g were charged into a1-liter 4-nozzle separable flask provided with a thermometer, a coolingpipe, and the mixture was a stirrer, and heated to 80° C. with stirringso as to be dissolved. Next, after charging 2,2-bis(4-cyanatophenyl)propane (Arocy B-10, a trade name of a product of Asahi Ciba Co.) 75 g,p-(α-cumyl) phenol 15 g, and triphenylcyanulate bromide (PyroguardSR-245, a trade name of a product of Dai-ichi Industrial Chemical Co.)45 g into the flask so as to be dissolved, 0.7 g of a toluene solutionof 10% by weight of cobalt naphthenate (content of Co=8% by weight, aproduct of Japan Chemical Industry Co.) was added to the reactionliquid, and reacted at a reflux temperature for 2 hours. After coolingthe reaction liquid room temperature, a toluene solution of 10% byweight zinc naphthenate (content of Zn=8% by weight, a product of JapanChemical Industry Co.) 0.1 g was added and dissolved by stirring toobtain a modified cyanate ester group curable resin composition varnish(solid content=31 weight %).

Similarly, the modified cyanate ester group curable resin compositionvarnish of embodiments 14-18, and the comparative examples 5, 7 weremanufactured using the composition indicated in Table 3.

Using the composition indicated as comparative example 6 in Table 3, themodified cyanate ester group curable resin composition varnish ofembodiment 12 was manufactured.

Methyl ethyl ketone (MEK) 240 g, 2,2-bis(4-cyanatophenyl) propane (ArocyB-10, a trade name of a product of Asahi Ciba Co.) 120 g, p-(α-cumyl)phenol 2 g, and 40 g of bromated bisphenol A type epoxy resin (ESB, atrade name of a product of Sumitomo Chemical Industries Co.), which wasreactive with a cyanato group, as a flame retardant were charged into a1-liter 4-nozzle separable flask provided with a thermometer, a coolingpipe, and a stirrer. After dissolving the charged chemicals withstirring, 1.2 g of a toluene solution of 10% by weight of cobaltnaphthenate (content of Co=8% by weight, a product of Japan ChemicalIndustry Co.) was added to the reaction liquid, and reacted at a refluxtemperature for 2 hours. Then, the reaction liquid was cooled to roomtemperature to obtain a varnish (solid content=40 weight %)

A resin film adhered with a film made of polyethylene terephthalate(PET) having a resin layer 30-33 μm thick was manufactured by applyingthe manufactured varnish, respectively, onto a film made of PET (BurexA-63, a trade name of a product made by Teijin Co.) of 50 μm thick witha releasing agent using a comma type coater (made by Hirano techseedCo.), a kind of bar coater, and dried at 130° C.

The manufactured modified cyanate ester group curable resin films of theembodiments 11-18, and the comparative example 5 had no resin cracks norpowder spilling even when the film was cut by a cutter-knife, and thefilms were found to be superior in handling properties.

On the contrary, resin cracks and powder spilling were generated whenthe resin film of the comparative example 6 was cut by a cutter-knife,and the resin film could not be handled if the resin film was separatedfrom the PET film.

Separated coagulation of the polyphenylene ether resin was observed inthe varnish of the comparative example 7 after a day elapsed, and noresin film could be manufactured.

TABLE 3 (B) (C) (E) Sol- (A) Mono- Polyphenyl- (D) Metallic id Cyanatevalent ene Flame reaction con- ester phenol ether retardant catalysttent Emb¹⁾ Com²⁾ Mix³⁾ Com. Mix. Com. Mix. Com. Mix. Com. Mix. wt % 11B-10 80 PCP 2 PPO 160 BC- 60 Mn 0.3 32 PCP 6 48 Zn 0.2 12 B-10 80 POP 2PPO 160 BC- 60 Mn 0.3 32 PBP 5 48 Zn 0.2 13 B-10 75 PCP 15 PPO 105 SR-45 Co 0.7 31 245 Zn 0.1 14 B-10 75 POP 15 PPO 105 SR- 45 Co 0.7 31 245Zn 0.1 15 B-10 90 PCP 11 PPO 90 CD- 35 Mn 0.7 30 75P 16 B-10 90 POP 11PPO 90 CD- 35 Mn 0.7 30 75P 17 M-10 120 PCP 6 PPO 60 BCL- 30 Mn 0.4 29462 Co 0.2 18 M-10 120 PAP 6 PPO 60 BCL- 30 Mn 0.4 29 462 Co 0.2 C-5⁴⁾ —— — — PPO 120 BC- 20 — — 28 48 C-6 B-10 120 PCP 2 — — ESB- 40 Co 1.2 40400 C-7 B-30 90 NP 1 PPO 90 ESB- 60 Co 1.0 29 400

Remarks:

1) Emb; Embodiment number

2) Com.; Kind of compound

3) Mix.; Mixing ratio (parts by weight)

4) C-; Comparative example number

Next, the resin films adhered with the PET film of the embodiments 11-18were evaluated as to the handling properties of the resin film alone andthe solvent-resistance of the cured film.

The PET film was peeled off from the adhered resin film adhered with thePET film of the embodiment 11. Twelve sheets of the manufactured resinfilm were piled up, and a mirror plane of electrolyzed copper foil waspiled onto the respective upper plane and lower plane of the piled resinsheets as a peeling plane. Then, the piled sheets were pressurized with1.5 MPa at 200° C. for 1 hour to form a cured film of the modifiedcyanate ester group resin of approximately 0.4 mm thickness. Similarly,the resin films of the embodiments 12-18 were pressurized to formrespective cured resin films.

Regarding the resin film adhered with the PET film of the comparativeexample 5, the PET film was peeled off from the adhered resin film,twelve sheets of the manufactured resin film were piled up, and a mirrorplane of electrolyzed copper foil was piled onto the respective upperplane and lower plane of the piled resin sheets as a peeling plane.Then, The piled sheets were pressurized with 1.5 MPa at 200° C. for 1hour to form a cured film of the modified cyanate ester group resin ofapproximately 0.4 mm thickness.

A similar operation was performed on the resin film adhered with the PETfilm of the comparative example 6. However, the resin film adhered withthe PET film of the comparative example 6 was a film made of onlycyanate ester resin, and the resin film was broken when peeling of thePET film was attempted because the resin film itself was brittle.Therefore, a cured film of the resin could not be manufactured.

The above cured resin film was cut up into pieces 50 mm square, immersedinto toluene, and kept at room temperature for 60 minutes. No swellingnor changes in appearance could be observed on the cured resin films ofthe embodiments 11-18. Surfaces of the separately prepared cured resinfilms of the embodiments 11-18 were wiped several times with a clothwetted with toluene or methyl ethyl ketone (MEK), and changes inappearance of the film were observed. However, no changes could beobserved on the surface of the cured resin films of the embodiments11-18.

Similarly, the cured resin film of the comparative example 5 was up intopieces 50 mm square, immersed into toluene, and kept at room temperaturefor 60 minutes. Swelling of the film was observed, because the curedresin film was made of only polyphenylene ether, and a part of the filmwas dissolved. When a surface of the separately prepared cured resinfilm was wiped several times with a cloth wetted with toluene, thesurface of the film was dissolved, and became sticky. When a surface ofthe separately prepared cured resin film was wiped several times with acloth wetted with methyl ethyl ketone (MEK), cracks were generated onthe surface of the film, and finally the film was broken by generationof holes.

In accordance with the above results, it was confirmed that the modifiedcyanate ester group resin film of the present invention allowed handlingby the film alone, and exhibited a preferable solvent-resistance.

Embodiments 19-26, and comparative example 8

Fused silica powder having an average particle size of 5 μm 25 g wasadded as an inorganic filler to 170 g of the modified cyanate estergroup resin varnishes manufactured by the compositions indicated inTable 3; and further, 200 g of ceramic beads 1.0 mm in diameter wasadded to the mixture, and the mixture was kneaded at 1500 rpm for onehour using a bead mill made by AIMEX Co. After the kneading, the beadswere filtered off from the varnish, and a filler containing a curedresin film adhered with the PET film having a resin layer(including thefiller) of 55-60 μm thickness was manufactured by the steps of applyingthe varnish onto a polyethylene terephthalate (PET) film (PUREX A=63, atrade name of a product made by Teijin Co.) of 50 μm in thickness havinga releasing agent thereon using a comma type coater, a kind of barcoater, and was dried at 130° C.

Comparative example 8

A modified cyanate ester group curable resin composition varnish (solidcontent=30% by weight) was manufactured by the same method as theembodiment 15 except for replacing the p-(α-cumyl)phenol in theembodiment 15 with 2 g of nonyl phenol (made by Mitsui Toatsu Chemicalco.), and adding and dissolving 45 g of tetrabromobisphenol A (FireGuard FG-2000, a trade name of a product made by Teijin Chemicals Co.),which was reactive with the cyanato group, as a flame retardant. Usingthe above varnish, a filler containing a cured resin film adhered withthe PET film having a resin layer(including the filler) of 55-60 μm inthickness was manufactured by the steps of kneading fused silica powderwith the varnish, and then applying and drying it in the same manner asthe embodiment 15. The manufactured resin film had no resin cracks norpowder spilling even when the film was cut by a cutter-knife, and wassuperior in handling properties.

The PET film was peeled off from the adhered resin film adhered with thePET film of the embodiment 19. Twelve sheets of the manufactured fillercontaining resin film were piled up, and an electrolyzed copper foil 18μm in thickness was piled onto the respective upper plane and lowerplane of the piled resin sheets. The piled sheets were pressurized with1.5 MPa at 200° C. for 1 hour to form a cured resin composition ofapproximately 0.6 mm thickness having copper foils at both ends.Similarly, the filler containing resin films adhered with the PET filmof the embodiments 20-26 and the comparative example 8 were pressurizedwith electrolyzed copper foils 18 μm in thickness to form respectivecured resin compositions having copper foils at both ends.

Next, triplates-line oscillators having a line length of approximately200 nm were manufactured from these cured resin compositions havingcopper foils at both ends by chemical etching, and the dielectricconstants and the dissipation factors at 1 GHz were manufactured bymeasuring transmission loss in the 1 GHz band using a network analyzer.The glass transition temperature (Tg) and the tensile elastic modulus/40° C. were measured in a tensile mode (frequency; 10 Hz, temperaturerise; 5° C./min.) on the filler containing cured resin composition byremoving the copper foil by etching, and cutting out test pieces, with awide band viscosity-elasticity measuring apparatus (DVE, made byRheology Co.). The manufactured results are indicated in Table 4.

TABLE 4 Glass trans. Tensile Embodiment Dielectric properties temp.(Tg)elasticity (comp.)¹⁾ Diel. c.²⁾ D. f.³⁾ (° C.) (MPa) 19 (Emb.11) 2.70.0048 174 4700 20 (Emb.12) 2.7 0.0048 170 4690 21 (Emb.13) 2.7 0.0054176 4790 22 (Emb.14) 2.7 0.0056 172 4800 23 (Emb.15) 2.8 0.0044 178 541024 (Emb.16) 2.8 0.0044 180 5400 25 (Emb.17) 2.8 0.0045 188 5590 26(Emb.18) 2.8 0.0047 184 5550 27 (Emb.19) 3.3 0.0122 172 4240

Remarks:

1) Comp.; Composition

2) Diel. C.; Dielectric constant

3) D. f.; Dissipation factor

It was confirmed that the filler containing resin film using themodified cyanate ester group resin film of the present invention had lowdielectric properties in the GHz band, particularly a low dissipationfactor because the cyanate ester group compounds reacted with thespecified monovalent phenol group, a preferably glass transitiontemperature, which can be deemed as an index of heat resistance, and amechanical strength.

Embodiments 27-29, comparative examples 9, 10

In accordance with the embodiments 27-29, respective copper foil cladresin films having a resin layer of 60-70 μm in thickness wasmanufactured by applying respective modified cyanate ester group curableresin composition varnishes in the embodiments 11,13, and 15 onto aroughened surface of the electrolyzed copper foil of 18 μm in-thicknessusing a comma type coater, a kind of coater, and drying. Themanufactured resin film had no resin cracks nor powder spilling evenwhen the film was cut by a cutter-knife, and was superior in handlingproperties.

Then, respective ones of a four layer printed circuit board weremanufactured by the steps of piling up respective resin films having thecopper foils of the embodiments 27-29 at both end planes of an innercircuit board (copper foil thickness for circuit: 18 μm), which was acopper plated epoxy resin laminated board having a glass cloth basematerial whereon a conductive circuit was formed, so as to contactrespective resin layers with the inner circuit, and the pile waspressurized to form the four layer circuit board under a condition of200° C., 2.5 MPa for 60 minutes.

Similarly, using the varnish of the comparative example 8, a copper foilclad resin film having a resin layer of 60-70 μm thickness wasmanufactured by the same method as the embodiments 27-29, and a fourlayer circuit board was manufactured similarly as the comparativeexample 9.

In accordance with comparative example 10, a four layer printed circuitboard was manufactured by the steps of piling up respective ones of anepoxy resin prepreg (FR-4 grade) having a glass cloth base material fora multilayered circuit board having a nominal thickness of 70 μm, and acopper foil 18 μm in thickness was laminated at each of the end planesof the copper plated epoxy resin laminated board having a glass clothbase material, which was the same as the board used in the embodiments27-29, and the pile was pressurized to form the four layer circuit boardunder a condition of 180° C., 2.5 MPa for 60 minutes.

Moldability (presence of voids and blur), soldering heat resistance, andthe copper foil peeling strength of the four layer printed circuitboards manufactured by the embodiments 27-29, and the comparativeexamples 9 and 10, were evaluated by the following methods. The resultsare indicated in Table 5. (Evaluating methods of characteristics)

Moldability: All of the outer layer copper foil of the four layercircuit board was removed by chemical etching, and the filling conditionof the resin into the inner circuit (presence of voids and blurs) wasobserved by eye. ma Soldering heat resistance: A four layer board 50 mmsquare with the outer layer copper foil was floated onto molten solderat 260° C., and the time until a swell was generated was measured.

Copper foil peeling strength: The strength was measured substantiallybased on the method defined by JIS-C-6481.

Flame retardance: All the copper foils on the FR-4 grade substrate of0.2 mm thickness were etched, and the resin films having copper foils atboth end planes of the embodiments and the comparative examples werepressed for forming tests pieces. The test pieces were evaluatedsubstantially based on a method defined by the UL-94 vertical evaluatingmethod.

TABLE 5 Soldering heat Peeling Flame Embodi- resistance strengthretardance ment Moldability (sec.) (KN/m) UL-94 27 No void, no blur >1801.5 Equ.to V-0¹⁾ 28 No void, no blur >180 1.5 Equ.to V-0 29 No void, noblur >180 1.5 Equ.to V-0 C-9 No void, no blur 56 1.2 Equ.to V-0 C-10 Novoid, no blur >180 1.5 Equ.to V-0

As the table 5 indicates, it was confirmed that the copper foil cladresin film of the embodiments 27-29 had a desirable moldability as amaterial for a multilayered circuit board, and the four layer circuitboards using the copper foil clad resin film of the present inventionhad a desirable soldering heat resistance because the modified cyanateester group resin reacted with the specified monovalent phenoliccompound, and the resin film had the same characteristics as theconventional prepreg for adhesion using a glass cloth as a basicmaterial.

What is claimed is:
 1. A method of manufacturing varnish of a modifiedcyanate ester group curable resin composition which comprises the stepsof: dissolving (C) a polyphenylene ether resin into (F) an aromatichydrocarbon solvent with heating to provide a solution; and reacting (A)a cyanate ester group compound having two cyanate groups in a moleculewith (B) a monovalent phenolic compound in said solution in the presenceof (E) a metallic reaction catalyst to generate a mutually dissolvingsolution of a modified cyanate ester resin and a polyphenylene resin, anadded quantity of (B) the monovalent phenolic compound in said solutionbeing 4 to 30 parts by weight to 100 parts by weight of (A) the cyanateester group compound having two cyanate groups in the molecule, aquantity of (C) the polyphenylene ether resin in said solution being 5to 300 parts by weight to 100 parts by weight of (A) the cyanate estergroup compound having two cyanate groups in the molecule, wherein said(A) cyanate ester group compound is expressed by chemical formula (1),

where, R₁ is

 and R₂ and R₃ is any one of hydrogen or methyl group, and the both canbe the same or different from each other, and wherein said (B)monovalent phenolic group compound is expressed by chemical formula (2),or formula (3),

 wherein R₄ and R₅ is any one of hydrogen atom or low alkyl group having1 to 4 carbon atoms, and the both can be the same or different from eachother, n is a positive integer of 1 or 2,

 where, R₆ is any one of —CH, —CH₂CH₃,


2. A method of manufacturing varnish of a modified cyanate ester groupcurable resin composition which comprises the steps of: dissolving (C) apolyphenylene ether resin into (F) an aromatic hydrocarbon solvent withheating, to provide a solution; reacting (A) a cyanate ester groupcompound having two cyanate groups in a molecule with (B) a monovalentphenolic compound in said solution in the presence of (E) a metallicreaction catalyst to generate mutually dissolving solution of a modifiedcyanate ester resin and a polyphenylene resin, an added quantity of (B)the monovalent phenolic compound in said solution being 4 to 30 parts byweight to 100 parts by weight of (A) the cyanate ester group compoundhaving two cyanate groups in the molecule, a quantity of (C) thepolyphenylene ether resin in said solution being 5 to 300 parts byweight to 100 parts by weight of (A) the cyanate ester group compoundhaving two cyanate groups in the molecule, and suspending the mutuallydissolving modified cyanate ester resin and the polyphenylene resin byadding (G) a ketone group solvent to said mutually dissolving solution,wherein said (A) cyanate ester group compound is expressed by chemicalformula (1),

where, R₁ is

and R₂ and R₃ is any one of hydrogen or methyl group, and the both canbe the same or different from each other, and wherein said (B)monovalent phenolic group compound is expressed by chemical formula (2),or formula (3),

 wherein R₄ and R₅ is any one of hydrogen atom or low alkyl group having1 to 4 carbon atoms, and the both can be the same or different from eachother, n is a positive integer of 1 or 2,

 where, R₆ is any one of —CH, —CH₂CH ₃,


3. A method of manufacturing varnish of the modified cyanate ester groupcurable resin composition as claimed in claim 2, which comprises thefurther step of: dissolving (D) a flame retardant not reactive with thecyanate ester group compound into a reaction solution of (A) the cyanateester group compound with (B) the monovalent phenolic compound in thepresence of (E) the metallic reaction catalyst to generate the mutuallydissolving solution of the modified cyanate ester resin and thepolyphenylene resin.
 4. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 2, which comprises the further step of: dissolving (D) a flameretardant not reactive with the cyanate ester group compound into saidmutually dissolving solution of the modified cyanate ester resin and thepolyphenylene resin.
 5. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 2, wherein a part of total mixing amount of (B) the monovalentphenolic compound is reacted with the cyanate ester group compound inthe presence of (E) the metallic reaction catalyst to generate themutually dissolving solution of the modified cyanate ester resin and thepolyphenylene resin, wherein in the suspending step a suspended mutuallydissolving solution is provided; and wherein the method includes afurther step of adding and dissolving a residual of the total mixingamount of (B) the monovalent phenolic compound into said suspendedmutually dissolving solution.
 6. A method of manufacturing vanish of themodified cyanate ester group curable resin composition as claimed inclaim 2, wherein after suspending said mutually dissolving solution byadding and stirring (F) a ketone group solvent to form a suspendingsolution, (E) the metallic group reaction catalyst is further added intosaid suspending solution.
 7. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 2, wherein 100 parts by weight of (C) the polyphenylene etherresin is dissolved into 150-500 parts by weight of (F) an aromatichydrocarbon group solvent, with heating.
 8. A method of manufacturingvarnish of the modified cyanate ester group curable resin composition asclaimed in claim 1, wherein 100 parts by weight of (C) the polyphenyleneether resin is dissolved into 150-500 parts by weight of (F) thearomatic hydrocarbon group solvent, with heating.
 9. A method ofmanufacturing varnish of the modified cyanate ester group curable resincomposition as claimed in claim 2, wherein 50-500 parts by weight of (G)the ketone group solvent is used for 100 parts by weight of (F) thearomatic hydrocarbon group solvent, which is used for dissolving (C)said polyphenylene ether resin.
 10. A method of manufacturing varnish ofthe modified cyanate ester group curable resin composition as claimed inclaim 1, wherein (F) said aromatic group solvent has a boiling point inthe range of 70-170° C.
 11. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 2, wherein (F) said aromatic group solvent has a boiling point inthe range of 70-170° C.
 12. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 1, wherein (F) said aromatic group solvent is at least oneselected from the group consisting of toluene, xylene, ethylbenzene,isopropylbenzene and mesitylene.
 13. A method of manufacturing varnishof the modified cyanate ester group curable resin composition as claimedin claim 2, wherein (F) said aromatic group solvent is at least oneselected from the group consisting of toluene, xylene, ethylbenzene,isopropylbenzene and mesitylene.
 14. A method of manufacturing varnishof the modified cyanate ester group curable resin composition as claimedin claim 2, wherein (G) said ketone group solvent has a boiling point inthe range of 50-170° C.
 15. A method of manufacturing varnish of themodified cyanate ester group curable resin composition as claimed inclaim 2, wherein (G) said ketone group solvent is at least one selectedfrom the group consisting of acetone, methyl ethyl ketone, 2-pentanone,3-pentanone, methyl isobutyl ketone, 2-hexanone, cyclopentanone,2-heptanone and cyclohexanone.
 16. A varnish of the modified cyanateester group curable resin composition manufactured by said method asclaimed in claim
 1. 17. A varnish of the modified cyanate ester groupcurable resin composition manufactured by said method as claimed inclaim
 2. 18. A prepreg, manufactured by the steps of: impregnating saidvarnish of the modified cyanate ester group curable resin composition asclaimed in claim 17 into a base material, and drying at a temperature inthe range of 80-200° C.
 19. A prepreg, manufactured by the steps of:impregnating said varnish of the modified cyanate ester group curableresin composition as claimed in claim 16 into a base material, anddrying at a temperature in the range of 80-200° C.
 20. A modifiedcyanate ester group curable resin film, manufactured by the steps of:applying said varnish of the modified cyanate ester group curable resincomposition as claimed in claim 16 onto one plane of a supportingmaterial, by a flowing method, and heating and drying for removing thesolvent to form said film.
 21. A modified cyanate ester group curableresin film, manufactured by the steps of: applying said varnish of themodified cyanate ester group curable resin composition as claimed inclaim 17 onto one plane of a supporting material, by a flowing method,and heating and drying for removing the solvent to form said film.
 22. Ametal foil clad modified cyanate ester group curable resin film,manufactured by the steps of: applying said varnish of the modifiedcyanate ester group curable resin composition as claimed in claim 16onto one plane of said metal foil, by a flowing method, and heating anddrying for removing the solvent to form said film.
 23. A metal foil cladmodified cyanate ester group curable resin film, manufactured by thesteps of: applying said varnish of the modified cyanate ester groupcurable resin composition as claimed in claim 17 onto one plane of saidmetal foil, by a flowing method, and heating and drying for removing thesolvent to form said film.
 24. A metal foil clad laminated board,manufactured by the steps of: piling up at least one of said prepreg asclaimed in claim 19 to form a piled body; laminating said metal foilonto both end planes or one end plane of said piled body; andpressurizing said piled body laminated with said metal foil with heatingto form said metal foil clad laminated board.
 25. A printed circuitboard manufactured by forming a circuit onto said metal foil cladlaminated board as claimed in claim
 24. 26. A metal foil clad laminatedboard, manufactured by the steps of: piling up at least one of said filmas claimed in claim 22, to form a piled body; laminating said metal foilonto both end planes or one end plane of said piled body; andpressurizing said piled body laminated with said metal foil with heatingto form said metal foil clad laminated board.
 27. A printed circuitboard manufactured by forming a circuit onto said metal foil cladlaminated board as claimed in claim
 26. 28. A multilayered circuitboard, manufactured by the steps of: laminating a metal foil onto aninner layer circuit substrate via said prepreg as claimed in claim 19;connecting said metal foil with circuits in said inner layer circuitsubstrate; and patterning a circuit onto said metal foil.
 29. Amultilayered circuit board manufactured by the steps of: laminating saidmetal foil clad modified cyanate ester group curable resin film asclaimed in claim 22, onto an inner layer circuit substrate; connectingsaid metal foil with circuits in said inner layer circuit substrate; andpatterning a circuit onto said metal foil.
 30. A multilayered circuitboard manufactured by the steps of: laminating a metal foil onto aninner layer circuit substrate via said film as claimed in claim 20;connecting said metal foil with circuits in said inner layer circuitsubstrate; and patterning a circuit onto said metal foil.